1. Field of the Disclosure
This disclosure relates generally to oilfield downhole tools and more particularly to methods and devices for enhanced directional drilling of wellbores.
2. Description of the Related Art
To obtain hydrocarbons such as oil and gas, boreholes or wellbores are drilled by rotating a drill bit attached to the bottom of a BHA (also referred to herein as a “Bottom Hole Assembly” or (“BHA”). The BHA is attached to the bottom of a tubing, which is usually either a jointed rigid pipe or a relatively flexible spoolable tubing commonly referred to in the art as “coiled tubing.” The string comprising the tubing and the BHA is usually referred to as the “drill string.” When jointed pipe is utilized as the tubing, the drill bit is rotated by rotating the jointed pipe from the surface and/or by a mud motor contained in the BHA. In the case of a coiled tubing, the drill bit is rotated by the mud motor. During drilling, a drilling fluid (also referred to as the “mud”) is supplied under pressure into the tubing. The drilling fluid passes through the BHA and then discharges at the drill bit bottom. The drilling fluid provides lubrication to the drill bit and carries to the surface rock pieces disintegrated by the drill bit in drilling the wellbore. The mud motor is rotated by the drilling fluid passing through the BHA. A drive shaft connected to the motor and the drill bit rotates the drill bit.
In addition to vertically aligned wells, a substantial proportion of the current drilling activity involves drilling of deviated and horizontal wellbores to more fully exploit hydrocarbon reservoirs. Irrespective of the well profile, however, it is essential to place the well bore trajectory as precisely as possible to optimally produce hydrocarbons. Conventionally, a trajectory of a drilled wellbore is defined by measuring inclination and azimuth at discrete survey stations while drilling. From these angular measurements and together with the length of the drill string, the trajectory can be reconstructed. Azimuth and inclination may be measured by survey sensors positioned along the drill string. The bending of the part of the string where the sensors are placed may “sag” and cause the borehole centerline to not necessarily point in the same direction as the centerline of the MWD tool with the sensors.
The present disclosure addresses the need for systems and devices that correct for errors caused by misalignment, sag or bending in survey measurements.